Comparison of the effect of experimental parameters on the properties of spin-coated and inkjet-printed indium tin oxide films
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Sethuraman, Sivaramakrishna
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Abstract
Transparent conducting films (TCFs) are films of optically transparent and electrically conductive material. TCFs are typically used as electrodes in photovoltaic applications like solar cells, LCDs, etc. that call for low resistance electrical contacts while not blocking the incident light. Doped metal oxides are the most important TCFs since their conductivity and band gap can be tuned through doping. Indium tin oxide (ITO) or tin-doped indium oxide is the most widely used owing to its excellent optoelectronic properties and ease of fabrication. Solution processing is a simple and cost-effective approach to deposit thin films under ambient conditions with minimum material wastage. In this research, transparent conducting films of ITO were deposited on soda-lime glass and sheet glass substrates using a sol-gel ITO ink. Two deposition techniques, spin coating and inkjet printing were used to deposit single and multilayer ITO films. The processing parameters evaluated include the spin coating speed, inkjet printing drop spacing, ink concentration, temperature, and humidity of the ambient. The results were optimized to achieve the lowest sheet resistance and impedance magnitude for single-layer ITO films while maintaining high optical transparency and uniform surface morphology. High humidity values affect the substrate wetting property of the ITO ink and increase the possibility of hydrolysis during deposition, resulting in the formation of non-uniform surface patterns. A speed of 4000 rpm or more in the case of spin coating and a drop spacing of 150 µm or more in the case of inkjet printing are required to obtain a uniform ITO film with desirable electrical and optical properties. Once the optimum combination of parameters is obtained, we propose to further reduce the sheet resistance and impedance magnitude by more than two orders of magnitude through multilayer deposition and annealing in a reducing environment with minimal effect on the optical transmittance and surface morphology.
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2021-04-27
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